Numerous attempts to develop systems of variable valve actuation have focused either upon the rocker arm, or on the lifter. For instance, ways to lock components of multiple piece rocker arms together to allow operation of specific cam lobes (low lift, low duration, or high lift, high duration) on a single valve have been attempted. Others have used a rigid, collapsing follower to allow actuation of the connected valve in one mode, or allow the valve to remain closed in another.
These designs typically require the use of an additional spring return to ensure the follower maintains contact with the cam lobe as the cam engages the follower continuously. A simple system for allowing dynamic engagement or disengagement of a cam lobe on the camshaft would eliminate the need for additional hardware to control unneeded motion.